1. Field of the Invention
This invention pertains to novel biuret polyisocyanates which are useful in preparing non-yellowing polyurethanes.
2. Description of the Prior Art
A variety of biuret polyisocyanates have previously been prepared by reacting an organic diisocyanate with water (U.S. Pat. Nos. 3,124,605 and 3,903,127), formic acid (U.S. Pat. No. 3,350,438), tertiary alcohols (U.S. Pat. No. 3,358,010) monoamines (U.S. Pat. No. 3,392,183), diamines (U.S. Pat. Nos. 3,441,588 and 3,903,126), ureas (U.S. Pat. No. 3,367,956 and U.K. Pat. Specification No. 1,043,674), and other biuretizing agents (U.S. Pat. No. 3,903,127).
Biuret polyisocyanates react with compounds bearing active hydrogen to form polyurethanes, polyureas, etc., as illustrated by U.S. Pat. No. 3,201,372, the disclosure of which is incorporated herein by reference. The biuret polyisocyanate derived from hexamethylene diisocyanate is taught to be the preferred biuret polyisocyanate for use in making polyurethanes in U.S. Pat. No. 3,201,372.
The major problems associated with the prior art compositions and processes are: (1) extremely high viscosities, and (2) the formation of insoluble ureas when water was used as the biuretizing agent. Such insoluble materials must be filtered from the final product.